Colored polymeric microsphere toners

ABSTRACT

NOVEL METHOD FOR COLORING SMALL POLYMERIC PARTICLES BY DISPERSING THE PARTICLES IN AN AQUEOUS MEDIUM HAVING A SUFFICIENT AMOUNT OF A WATER MISCRIBLE ORGANIC LIQUID CAPABLE OF SWELLING THE POLYMER AND AN OIL SOLUBLE DYE SOLUBLE IN SAID ORGANIC LIQUID. BY AGITATING THE MIXTURE, THE DYE IS ABSORBED INTO THE POLYMERIC PARTICLES. THE PARTICLES ARE THEN WASHED FREE OF ANY UNABSORBED DYE AND ISOLATED.

United States Patent O 3,770,692 COLORED POLYMERIC MICROSPHERE TONERSDonald B. Miller, Menlo Park, Calif., assignor to Electroprint, Inc.,Palo Alto, Calif. No Drawing. Filed Oct. 29, 1971, Ser. No. 194,041 Int.CL (308i 45/66 US. Cl. 26041 C 14 Claims ABSTRACT OF THE DISCLOSURENovel method for colori'ng small polymeric particles by dispersing theparticles in an aqueous medium having a sufiicient amount of a watermiscible organic liquid capable of swelling the polymer and an oilsoluble dye soluble in said organic liquid. By agitating the mixture,the dye is absorbed into the polymeric particles. The particles are thenwashed free of any unabsorbed dye and isolated.

BACKGROUND OF THE INVENTION Field of the invention In a number of uses,small polymeric particles are employed which are required to have aconsistent shape. The particles are conveniently formed in this shapeduring polymerization of the monomer. Dyeing of the particles is limitedto methods, whereby the particle shape is not significantly affected.

Extremely small polymeric particles are employed in some electrostaticprinting systems. The ink or dye is incorporated into the particles andimparted to the paper in accordance with the electrostatic printingsystem. The dyed particles are called toner and the size of theparticles is rigidly restricted within fairly narrow limits. Inaddition, it is desirable that the particles have relatively uniformspherical shape.

Attempts to incorporate dyes during polymerization are normallyunsuccessful. The dyes act as inhibitors for the free radicalinitiators.

While grinding of dyed polymer can provide colored particles, obtainingnarrow size distribution is only difiicultly achieved. Furthermore, theparticles will tend to be irregularly shaped. Therefore, methods wherebyparticles can be formed of the desired size distribution during thepolymerization step and then dyed without modification of the polymericparticle structure are desirable.

SUMMARY OF THE INVENTION Small polymeric particles are dyed bydispersing the particles in an aqueous medium, usually with a wettingagent, combining the polymeric particle dispersion with a solution of anoil soluble dye in a water miscible solvent, where the water misciblesolvent is capable of swelling the polymeric particles, mildly agitatingthe system for a sutficient time for the desired amount of dye to beabsorbed by the particles, washing the particles free of unabsorbed dyeand isolating the particles.

By employing suspension polymerization to prepare the particles, theresulting polymeric dispersion may be used directly with a solution ofthe oil soluble dye.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS In accordance with the subjectinvention, small waterinsoluble polymeric particles are dyed bydispersing the particles, normally in the presence of a wetting agent,in an aqueous medium, having a water soluble swelling agent for thepolymer and an oil soluble dye. The mixture is then agitated for asufficient time for the polymeric particles to absorb the desired amountof the oil soluble dye.

Fee

In a preferred embodiment, the polymeric particles are first formed bysuspension polymerization, and a solution of the dye in the watersoluble polymer swelling agent added to the suspension polymerizationsystem after the particles have been formed.

After the particles have absorbed the desired amount of dye, theparticles are freed of any unabsorbed dye by thoroughly washing, usuallywith water, and the particles isolated and any residual dyesolvent-swelling agent present in the particles evaporated.

The temperature and pressure for the process is not critical and anyconvenient temperature and pressure may be employed, as long as theliquids remain fluid. Usually, the temperature will vary from about 15C. to C. The temperature employed should be below the boiling point ofboth water and the dye solvent.

While the amount of polymer dispersed in the aqueous system is notcritical, there should be enough water to permit the particles to flowsmoothly when agitated. Usually, there will be from about 0.5 to weightpercent of polymer based on water, more usually from about 5 to 50weight percent of polymer based on water. The amount of dye solvent willvary, usually depending on the particular solvent and its solubility inwater and ability to swell the polymer. Normally, there will be at leastabout 10 and not more than about 200 volume percent of dye solvent basedon water, more usually from about 15 to volume percent.

Since a major portion of the dye will normally precipitate out uponaddition of the dye solution to the aqueous suspension, large excessesof dye may be employed. However, this is inefllcient, and normally fromabout 0.5 to 25 weight percent of dye based on polymer will be employed,more usually from about 1 to 20 Weight percent.

Also, small amounts of other agents, such as suspending agents and/ orwetting agents may be used advantageously. The total amount of wettingagent will usually be in the range of from about 0.1 to 5 weightpercent, more usually 0.5 to 4 weight percent based on water. The totalamount of suspending agent, which is usually present as part of thepolymerization process will be in the range of from about 0.05 to 5weight percent based on water.

The order of addition is not critical as long as the dye is added to theaqueous system as a solution in the dye solvent. Therefore, anyconvenient method of combining the various materials may be employed.Mild agitation is used so as to enhance the continuous absorption of thedye into the swelled polymer and maximize the polymeric surface exposedto the dye. The time may be varied widely depending on the system used,usually being at least about 10 minutes and not exceeding 60 hours, moreusually being from about 0.5 hours to 30 hours.

Having discussed the process, the individual materials will beconsidered. A wide variety of water insoluble polymers may be employed.For the most part, the polymers are addition polymers which have beensynthesized by free radical polymerization and may be prepared by anyconvenient means. This includes polymerization neat or in an inertsolvent, suspension polymerization and emulsion polymerization. However,a preferred embodiment is to employ suspension polymerization, where theaddition polymerizable monomer is dispersed in water in the presence ofa free radical catalyst and a dispersant or wetting agent. Suspensionpolymerizations are Well known in the art and do not require extendeddiscussion here.

Polymers which may be employed include methacrylates, acrylates,styrene, alpha-methylstyrene, vinylesters, polyenes, vinylhalides,vinylethers, etc. Specific exemplifications include methyl methacrylate,ethyl acrylate,

3 styrene, vinyl ethyl ether, vinyl butyrate, vinyl chloride, vinylidenechloride, either individually or in combination as co-polymers. Themonomers will usually be of from 2 to 24 carbon atoms.

The particles will usually be of at least one micron and 4 5 I}colorless commercial poly(ethyl methacrylate) molding resin consistingof 20-200n particles (mostly 75-150p. particles) was suspended in waterand treated with a solution of BASF deep Black BB dye intetrahydrofuran. After following the above workup procedure, theprodusually not greater than 0.2 mm. in diameter. For toners, 5 uctconsisted of black, opague microspheres, whose size the particles willusually be in the range of 5 to 50 and size distribution were notappreciably changed by microns in diameter. the coloring treatment. v

A wide variety of solvents for the oil soluble dye may be employed,which are miscible in Water at the EXAMPLE HI amounts used. Usually thiswill require that the dye sol- A suspension of I P y y microspheles ventbe soluble to the extent of at least 10 weight percent (Diamond Shamrockdiluted with based on water, more usually about 25 weight percent water110 105 m1. and treated While stirring, With 1.8 g. based on water, andpreferably the dye solvent will be BASF D6619 Black 1313 ye i 20 mStirring miscible with water at all ratios. Illustrative solventsinhours at the lIliXtllle Was fi e and t e lid elude acetone,tetrahydrofuran, dioxane, pyridine, acetic as Washed three times WithWater in a high speed blenderacid, methanol, isopropanol,dimethylacetamide, etc. The The y Product consisted f y of black"preferred solvents are oxygenated solvents, particularly Opaque ornearly opaque 5-20 t microspheres. alcohols, ethers and ketones. Thesolvent will have a 1 solubility parameter similar to that of thepolymer em- 20 ployed, usually within three whole numbers of the solu-Example 3 was repeated wlth ldentlcal Procedure except bili parameter fh l that acetone (20 ml.) was the solvent for the BASF BB Substantiallyany oil soluble dye may be employed After several hours at the P y y p fhi h i 1 1 1 in the swelled po1ymer various 11 were not swollen orcolored extensively, and much uninsoluble dyes include BASF oil solubledeep black BB, 25 p t black was shh Present in the suspension- Keystoneoil black BT, Orasol Black 2RG, Oracet Blue An addmonal 80 acetone wasthen added to the B, m mixture and stirring was continued about 20hours. The The only other materials employed are wetting or susmiXtlJrewas filtered, and the solid was washed three pending agents. The wettingand suspending agents may times with water in a high pe blendsr- The beanionic, cationic or nonionic, but are preferably P 8-) cohsistedlargelyof 1 black P t anionic. The anionic agents include carboxylates, sulr yp q e m spheres. fonates, and sulfates, particularly as their sodiumsalts. EXAMPLE v I I A small amount of a higher alkanol e.g. octanol,may r be added with advantage to the aqueous medium, usually Rapldlyshrnhg a mlxture of (1) Y 1 to 20 drops per 100 ml. of water. Thealkanol acts as 100 a s methyl h h h: an tif i agent benzoyl peroxide,and 12 drops N,N-d1methylan1l1ne, and The following examples are ofieredby way of illustraallowmg to stand 3 hours gave a shsPensmh of tion andnot by Way f limitation. mostly 5- 15;t poly(methyl methacrylate)microspheres. (All temperatures when not indicated are centigrade). Tothe shlred shspehsloh was then added BASF 4 Deep Black BB in 25 ml. THF.After stirring 20 hours the EXAMPLE 1 mixture was filtered, and thesolid washed with water in a A suspension of poly(ethyl methacrylate)microhigh speed blender. The dried product (17.0 g. consisted spheres5-20 1. in diameter was prepared by adding a largely of opaque or nearlyopaque black poly(methyl mixture of 58.2 g. ethyl methacrylate, 0.4 g.benzoyl methacrylate) microspheres. peroxide and 10 dropsN,N-dimethylaniline to a mixture Following the above procedure,additional runs were of 250 ml. water, 3 g. Acrysol A-5 and 1.0 ml. 3%carried out. These runs are tabulated in the following Aerosol OT, thenstirring rapidly under nitrogen until table.

Bus- Water, Recovered Parts Particle pending Parts Wetting Parts partsParts 801- Parts polymer, Polymer by wt. size, agent; bywt. agent; bywt.Octanol by wt. Dye bywt. vent by wt. parts 6. EMA 13 5-25 AAE 2.5 AO'I85 PR 0.2 M 25.- 7.IBMA 5 5-25 AAE 1 85 BB 0.5 A 25 5.5 s. IBMA...- 55-25 AA5 1 85 BB 0.5 a 25 5.1 9. Vs 5 15-35 AAE 1 80 BB 0.5 a 35 5.7 10.vs--- 5 15-35 AAE 1 80 BB 0.5 A 35 5.8 11. BMA/IBMA 1) 7 5-20 AAE 1 80KB 0.7 A 30 7.7 12. BMA/IBMA 1:1 7 5-20 AAE 1 80 {gg 3:7, }A 40 6.3

1 EMA=Ethyl methacrylate; IBMA=Isobutyl methaerylate; VS =Vinylstearate; BMA=Butyl mcthacrylate.

I AA5 =Acrysol A5 (polyacrylic acid) I AOT=disodio dioctylsulfosucclnateT=Tamol 731, sodium salt of polymeric carboxylic acid; D =Darvan 1,alkaryl sulfonate. PR=Peroxide red; BB =BASF oil solvent deep black BB;KB =Keystone oil black BT; 0BI=Orasol Black 2RG.

5 M=Methanol; A=Acetone. well dispersed, and then standing over night at25. A solution of 5 g. BASF Deep Black BB dye in 69 ml. THF was thensquirted into the well stirred, light colored suspension with a syringe.

After stirring slowly for about .20 hours, the mixture was diluted withseveral times its volume of water, stirred a little longer and thenfiltered. The dark filtrate was discarded and the black polymer waswashed several additional times by fast stirring in a blender. The dryisolated product weighed 53 g. and consisted principally of 5-20,u.opapue black spheres. The product performed exceptionally well in a dryelectrostatic copying process.

EXAMPLE II It is evident from the above results, that the subject methodprovides a convenient way for dyeing polymeric particles of relativelysmall size without affecting the parvticle shape or particle sizedistribution. The method is easily carried out in a convenient manner,particularly where the polymer has been prepared by suspensionpolymerization. In that event, the solution of dye may be added directlyto the suspension polymerization medium after completion of thepolymerization. Since solubility parameters are known for both solventsand polymers, the choice of solvent is easily made in accordance withthe choice of polymer. The only other considerations meme solubility ofthe dye in the solvent and the solubility of Following the dyeingprocedure of Example I, a the dye solvent in the water. r

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the invention, as limited only bythe scope of the appended claims.

What is claimed is:

1. A method for dyeing small particles of water insoluble polymer whichcomprises combining a dispersion of the particles in water with asolution of an oil soluble dye in a water soluble organic solventmedium, wherein said solvent is capable of swelling said polymer, for atime sufiicient for said polymer to absorb a significant amount of saiddye, and freeing said particles of unabsorbed dye and isolating saidparticles.

2. A method according to claim 1, wherein a small but sufiicient amountof a wetting agent is present.

3. A method according to claim 1, wherein said polymer is polystyrene, apolyacrylate, a polymethacrylate, a polyvinylester, a polyvinylether, ora polyvinylhalide.

4. A method according to claim 1, wherein said dye solution has anoxygenated organic solvent as the solvent.

5. A method according to claim 4, wherein said oxygenated solvent is aketone, ether, or alcohol.

6. A method of dyeing small particles of water insoluble polymer whichcomprises combining a dispersion of said particles in water with asolution of an oil soluble dye in a water soluble organic solventmedium, wherein said organic solvent has a solubility parameter withinthree whole numbers of the solubility parameters of said water insolublepolymer and is present in an amount based on water in from to 200 volumepercent and wherein from 0.1 to 5 weight percent based on water of awetting agent is present.

7. A method according to claim 6, wherein said wetting agent is ananionic dispersant.

8. A method according to claim 6, wherein said organic solvent is anoxygenated solvent, wherein said oxygen is present as a ketone, ether oralcohol functionality.

9. A method according to claim 8, wherein said oxygenated solvent isacetone.

10. A method according to claim 8, wherein said oxygenated solvent istetrahydrofuran.

11. A method according to claim 6, wherein said Water insoluble polymeris an addition polymerized polyester.

12. A method according to claim 11, wherein said polyester is amethacrylate.

13. A method according to claim 11, wherein said polyester is a vinylester.

14. A method according to claim 6, wherein said polymer is prepared bysuspension polymerization and said solution of said oil soluble dye in awater soluble organic solvent medium is added to the suspensionpolymerization system.

References Cited UNITED STATES PATENTS 3,326,848 6/1967 Clemens 26034.22,119,189 5/1938 Widmer 26039 P 2,467,055 4/ 1949 Sans 26034.2 2,710,8496/1955 Siggel 26040 P OTHER REFERENCES Handbook of Chemistry andPhysics, 47th edition, 1967, pp. C-331 and C-505.

MORRIS LIEBMAN, Primary Examiner P. R. MICHL, Assistant Examiner U.S.C1. X.R. 8-4; 26034.2

